Duck Trouble

My female duck hatched 9 ducklings on June 10th. The male duck became very aggressive, chasing them and pulling out feathers. I removed him from the enclosure but I am wondering when or if it will be safe to put him back in. I have tried to reintroduce him now that the ducklings are bigger but he constantly chases them and tries to mount the females. It seems like he is trying to get the ducklings away from the mother, but he doesn't try to mount her. I have tried to put just the female and the male together, but she stresses out about being away from the babies.
Help, is this normal? What should I do?

That is very normal. Your drake should be separated from the rest until the babies are fully feathered and just about grown. Let the mom raise her babies alone. The drake will be fine. He may moom around the fenceline, but he will be ok apart from the rest for a while. Drakes are terrible fathers. They don't help with the raising of the ducklings like ganders do with goslings. It is just not in their nature.

The probable sire rejoined the duck, ignoring the babies. Since then he seems to have figured out she wasn't putting out anymore and he spends most of his time with the rest of the bevy. Our big rouen drake will ignore the ducklings, but is relentless in trying to mate with their mother (we're going to try to rehome him at this year's county fair). Our other campbell drake seems to largely ignore them.

We also got five rouen ducklings, ~2 weeks older then ours, this spring. When they were set free, they picked on the younger ducklings for a while, and were in turn picked on by the mother duck. Just part of figuring out the pecking order, IMHO.